[net-next PATCH] net: ethernet: stmicro: stmmac: permit MTU change with interface up

[Christian 'Ansuel' Marangi]

Remove the limitation where the interface needs to be down to change
MTU by releasing and opening the stmmac driver to set the new MTU.
Also call the set_filter function to correctly init the port.
This permits to remove the EBUSY error while the ethernet port is
running permitting a correct MTU change if for example a DSA request
a MTU change for a switch CPU port.

Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth at gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index d1a7cf4567bc..a968a13b3183 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5448,11 +5448,6 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 
 	txfifosz /= priv->plat->tx_queues_to_use;
 
-	if (netif_running(dev)) {
-		netdev_err(priv->dev, "must be stopped to change its MTU\n");
-		return -EBUSY;
-	}
-
 	if (stmmac_xdp_is_enabled(priv) && new_mtu > ETH_DATA_LEN) {
 		netdev_dbg(priv->dev, "Jumbo frames not supported for XDP\n");
 		return -EINVAL;
@@ -5466,6 +5461,14 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 
 	dev->mtu = mtu;
 
+	if (netif_running(dev)) {
+		netdev_dbg(priv->dev, "restarting interface to change its MTU\n");
+		stmmac_release(dev);
+
+		stmmac_open(dev);
+		stmmac_set_filter(priv, priv->hw, dev);
+	}
+
 	netdev_update_features(dev);
 
 	return 0;
-- 
2.36.1